What a fabric measure gives the house in winter: less heat leaving it. Insulation, airtightness, better glazing and closed thermal bridges all deliver this, and it is the cheapest heat in any house because it is heat never lost. DELIBERATELY NOT QUANTIFIED. How much any one measure saves depends on what it is applied to and what was there before, which no source states per technique. So this carries no figure and never enters a verdict: it exists so the measure can be placed in the graph and named, rather than sitting outside it.